The present invention relates to a real image type finder optical system provided, in a camera, independently of a photographing optical system, and more specifically, to a real image type finder optical system which is capable of displaying information in the field of view thereof.
A real image type finder is known as one of finders provided in a camera. The real image type finder may be provided independently of a photographing optical system. The real image type finder includes an objective optical system having a positive power, an erecting optical system for erecting a reversed image formed by the objective optical system, and an eyepiece optical system for observing the erected image in a magnified fashion. The above described optical systems are provided in this order from an object side.
In general, the real image type finder is provided with an information displaying element in the vicinity of an image plane of the objective optical system to display information in the finder field. The displaying element is arranged such that an opaque pattern is formed on a portion of a transparent member to thereby shield light which is incident from an object so that a frame indicating a photographing range, a frame indicating a focusing zone, a photographing mode of the camera, and other alphanumeric information are displayed in the finder field. If the information is variable, a liquid crystal display element or the like may be used.
In the above-described conventional real image type finder, however, since the display element is disposed in the vicinity of the focusing surface of the objective optical system on which the eye of a viewer is focused, there is a problem that when foreign particles such as dust particles are adhered on the displaying element while it is assembled into the camera, the foreign particles may be made conspicuous in a field of view when observed through the eyepiece optical system. If the number of surfaces arranged in the vicinity of the image plane is reduced, the possibility that the foreign particles are made conspicuous in the field of view is reduced. For this purpose, there has been known an arrangement that the lens of the objective optical system is spaced from the vicinity of the image plane. However, since conventional finders are designed such that the patterns formed on a displaying element are directly observed through the eyepiece optical system, the displaying element cannot be positioned apart from the vicinity of the image plane for the clear observation of the patterns. Thus, there still remains a problem that the foreign particles are conspicuous in the field of view and prevent observation.